The present invention relates to the measurement of tension in filamentary material and, in particular, to the measurement of staple tow tension on a staple drawframe.
In the manufacture of synthetic filamentary material such as yarn, filaments are drawn from a die and combined to form the yarn, or tow, which may then be conducted to various treatment zones on a drawframe. As the tow is being conducted, it is important that the degree of tension which is imposed upon the yarn lie within a certain acceptable range. Devices for measuring tow tension have been heretofore proposed and typically involve a roll or the like which is maintained in engagement with the traveling tow to deflect the tow from what would otherwise be its normal path of travel. In so doing, a reaction force is transmitted from the tow to the roll. As the tension imposed on the tow varies, the roll will be displaced, the extent of which is measured by a suitable measuring instrument. That measurement enables the tension on the tow to be determined.
The roll is usually attached to the end of a moment arm, the latter being deflected by the roll displacement to enable measurements to be made. In practice, however, the amount of deflection of the arm may vary, depending upon the location of the yarn on the roll. That is, as the yarn shifts along the roll during travel (a common occurrence), the measurements may vary. Thus, the known measuring devices are inconsistent and prone to error.
Also, the measuring devices used in connection with so-called "jumbo" drawframes which handle high denier tow, require that large, heavy rolls be employed. The weight of such rolls is so great that distortions in measurements can result, especially if long torsion bars are employed which perform sensing as well as roll-support functions.
Furthermore, known measuring devices are generally rather large in size, making it difficult to retrofit existing drawframes wherein space is at a premium. Thus, the making of tow tension measurements on such existing drawframes may be rendered impacticable for that reason.
It is, therefore, an object of the present invention to minimize or obviate problems and shortcomings of the above discussed sort.
Another object is to provide an improved tow tension measuring apparatus which is highly accurate and insensitive to shifting of the path of travel of the tow.
A further object is to provide such a device which occupies little space so as to be capable of being retrofit onto existing drawframes.